1. Field of the Invention
The present invention relates to a method of assembling photographic film cassettes, and an apparatus for practicing the method.
2. Related Art
Photographic film of the 135 type, contained in a cassette, is among the most popular formats of photographic film. A known 135 photographic film cassette has a cassette shell constituted of a cylindrical body, formed from a thin metal sheet, and two caps fitted thereon. The cassette has a spool contained therein on which photographic film is wound in a form of a roll. To assemble this photographic film cassette, several methods are known. For example, U.S. Pat. No. 4,614,019 (corresponding to JPB 2-691) discloses a process of winding the photographic film on the spool, and then assembling the cassette in a darkroom; U.S. Pat. No. 4,080,711 (corresponding to JPB 60-48748) discloses a process of bringing the assembled cassette shell into the darkroom, disassembling the cassette shell for insertion of the photographic film, inserting the photographic film wound on the spool, and then assembling the cassette shell.
U.S. Pat. No. 4,834,306 (corresponding to JPA 1-306845), U.S. Pat. No. 4,846,418 and European Publication EP-A2 0 406 815 (corresponding to JPA 3-37645), each disclose a photographic film cassette in which a cassette shell is constituted of parts formed from resin, and rotation of a spool causes a leader of the photographic film to exit to the outside of the cassette. Such a leader-advancing cassette is different from conventional photographic film cassettes because the leader of the photographic film is fully contained within the cassette both before exposure and after exposure. Such a cassette is advantageous in that the photographic film is reliably protected from accidental exposure to ambient light, and in that the cassette is easily handled.
Such a leader-advancing cassette includes elements not utilized in conventional cassettes. As disclosed, for example, in U.S. Pat. No. 4,834,306 and U.S. Pat. No. 5,049,912, a light-shielding shutter member may be mounted openably in a photographic film passage port of this type of film cassette for protecting the inside from ambient light. Or a visual indicator member may be incorporated in such a cassette, to appear externally for indicating the exposed condition of the photographic film. However, production of such a leader-advancing cassette has many inherent problems due to the increase in the number of the parts. Particularly when the cassette shells must be assembled or disassembled in a dark room, the assembling operation is so complicated that efficiency of production is difficult to increase. In such a case, even an automated assembling machine does not reliably increase production efficiency in view of maintenance and repair.
The problems are more complicated in a case of a photographic film cassette wherein a spool is an assembly constituted of a pair of flanges force-fitted on the spool core, and the spool assembly is mounted in one shell half before the other shell half is joined therewith. This is because an independent assembling process for assembling the spool assembly is necessary before a primary assembling process of the film cassette, wherein the spool assembly, the shutter plate and other parts are mounted into the cassette shell. In such a case, there are at least two assembling lines and at least a transfer conveyor for connecting the two lines. Therefore, the mechanisms of the conventional systems are complicated. The need for transferring works between the lines increases the occurrence of problems.
To solve the above problems, an improvement is suggested in U.S. Ser. No. 08/233,261 (filed on Apr. 26, 1994), which uses a pallet 80 having a spool holder 81 and a shell holder 82 thereon as shown in FIG. 9. A plurality of such pallets 80 are successively conveyed along an assembling line, while parts of a cassette shell are sequentially fed to the pallet 80, wherein the parts of a spool assembly 83 are assembled in the spool holder 81 while its spool core is oriented in a vertical position, and that the complete spool assembly 83 and other parts are assembled into the cassette shell in the shell holder 82 while the axis of the cassette shell is horizontal. Since the spool assembly 83 is moved from the spool holder 81 to the shell holder 82 of the same pallet 80 after a shell half 84 is placed in the shell holder 82 on the same assembling line, it is unnecessary to provide two assembling lines. Because of the single assembling line, it is unnecessary to provide interconnecting devices which would otherwise be necessary for connecting primary and secondary assembling lines.
On the other hand, taking account any variability between lots of each kind of work pieces, a high accuracy, e.g., 0.55 mm or so, is necessary when mounting the spool assembly 83 in the shell half 84. However, for mounting the spool assembly 82 held in the spool holder 81 into the shell half 84 held in the shell holder 82 of the same pallet 80, it is necessary to move a chuck member or robot hand 85 of a chuck unit 86 in many directions after the chuck member 85 nips the spool assembly 83. That is, the chuck member 85 moves up in a vertical direction relative to the pallet 80, hereinafter referred to as Z-axis direction, to pull the spool assembly 83 off the spool holder 81, and then rotates through an angle of 90.degree. to orient the spool assembly 83 horizontal and parallel to an axial direction of the shell half 84 held in the shell holder 82, hereinafter referred to as Y-axis direction. Thereafter, the chuck member 85 moves in a direction toward the shell holder 82, hereinafter referred to as X-axis direction, to locate the spool assembly 83 in a position right above the shell half 84 in the shell holder 82. Next, the chuck member 85 should move in the Y-axis direction so as to position the spool assembly 83 relative to the shell half 84. Then, the chuck member 85 moves down and releases the spool assembly 83 to put in the shell half 84.
Accordingly, the chuck member 85 requires a complicated and relatively large scale chuck drive mechanism 86. Besides that, many directional movements makes it difficult to ensure the high accuracy necessary for mounting the spool 83 in the shell half 84. If the shell half 84 has hooks 84a for engagement with a counterpart shell half, as the hooks 84a protrude upwards from the shell holder 82, the chuck member 85 must not interfere with the hooks 84a. Therefore, the spool assembly 83 should be dropped from a higher position into the shell half 84, or the chuck member 85 must be narrower than the spacing between the hooks 84a. This lowers the stability and hence the accuracy of assembly operation.
To avoid the above described problems, it may be possible to mount the spool assembly 83 in a shell half 84 that is held in a shell holder 82 of another pallet 80, by transferring the spool assembly 83 from one pallet to another directly or through a transit station disposed besides the pallet conveyer. In either case, however, the amount of movement of the spool assembly 83 to be made within a transport step is so large that the maximum acceleration will increase, for instance, up to about 1.8 Gs when the interval between transport steps of the pallet conveyer is 1 second. The larger acceleration is disadvantageous in terms of mechanical construction.
Also a conventional double-hand system using two chucks cannot be adopted in the assembling system as shown in FIG. 9, since each pallet has the spool holder and the shell holder so as to allow the spool assembly to be assembled on the same pallet that is used for assembling the other parts of the cassette shell.
The above Y-axial movement of the chuck member 85 can be omitted if the spool assembly 83 is rotated by 90.degree. about its longitudinal center or half-length position. However, because of limited dimensions, it is difficult to design the chuck unit 87 to turn the spool assembly 83 about the longitudinal center thereof without any deviation.
It might be possible to shift the spool holder from the center of the shell holder in the Y-axis direction so that the spool assembly need not be moved in the Y-axis direction. However, this is not preferable because such a pallet tends to lose balance especially when the flange is force-fitted to the spool core or when the shell halves are force-fitted to each other. Also, the pallet must be widened correspondingly.